Secondary or storage batteries are made up of an electrochemical cell or cells that generate electricity. Rechargeable storage batteries can be recharged by passing a current through them in the reverse direction. The voltage or force generated by the recharging process depends on the number of cells that make up the battery. Normally each cell produces 2.05 volts. Cells may be connected in a series to create a battery with greater voltage, although the amperage or current is only the current of the one cell. Should greater current be required, the cells may be arranged in a parallel connection where the current is then the summed current of the cells. In this configuration, however, the voltage is only that of one cell, or the sum of the voltages across any cells which are connected in series (if any). In many cases, storage batteries are restricted to producing six or twelve volts.
Common drawbacks with such batteries include the short battery life between charges and the limited set of voltage and current configurations. These drawbacks are some of the major reasons why these batteries are not used extensively as stand-alone power sources. Electric cars, for example, would benefit enormously from a long-lasting battery which is powerful, economical and lightweight. But to date, existing batteries do not provide sufficient power over time to make the range and speed of such a car economically viable. The batteries now used to run completely electric cars are heavy, expensive and must be recharged every 50 to 75 miles. Consequently, electrically powered cars are slow, suffer from limited acceleration and have a short range. Additionally, the batteries lose their efficacy after a certain number of recharge cycles and must be replaced at great expense.
Storage batteries generate electricity through a chemical process that occurs at their electrode plates. For example, modern lead-acid batteries are made up of a positive and a negative grid that are separated from each other by a porous insulator which may be comprised of such materials as fiberglass, plastic, rubber or wood. The grids are made up of lead and lead-alloy plates and are generally cast grids covered by lead-paste or other compounds. The plates are submerged in an electrolyte solution of water and usually sulfuric acid. An electrochemical reaction creates a positive charge on the lead alloy plates and a negative charge on the lead plates. The negative plates are connected to the negative terminal and the positive plates are connected to the positive terminal. The plates are suspended in a plastic or glass composition container where the diluted sulfuric acid is introduced as an electrolyte.
Electricity is created during discharge by way of an electrochemical reaction. Due to the characteristics of the metals, separated by the conducting liquid, electrons migrate. The electron migration creates a voltage potential, which upon discharge generates an electric current. During the electrochemical reaction, the sulfuric acid electrolyte is converted to water as lead sulfate forms on the plates. Hydrogen gas is the byproduct of this reaction. The amount of charge remaining in the cell can be determined by measuring the specific gravity of the electrolyte compared to water. When the plates are fully coated with lead sulfate and the sulfuric acid has been converted to water, the battery is considered fully discharged.
Fully discharging such a battery, as described above, occurs relatively quickly. As a result, the battery can be used only for short bursts of energy, such as starting a car, or for relatively low electrical demand requirements, such as powering lights, before recharge is required. These drawbacks are why such batteries have not proven particularly successful in such electrically powered devices as fully battery-driven automobiles.
Recharging involves passing a current through the battery so as to reverse the chemical reactions at the electrodes and in the sulfuric acid mixture. Recharging tends to restore the electrode plates to their original state and reconstitute the sulfuric acid mixture. If the cell is overcharged, however, electrolysis of water occurs, creating oxygen and hydrogen. Should electrolysis happen, water must be added to the battery in order to recreate a properly constituted electrolyte solution of water and sulfuric acid. Furthermore, electrolysis creates a potentially dangerous condition with possible disastrous consequences since both hydrogen and oxygen are highly explosive gases.
Storage batteries usually have exposed positive and negative terminals that are directly attached to the battery. Such terminals tend to corrode which reduces current and voltage generation.
When used to start and operate devices such as lights or engine-driven devices, storage batteries are continually recharged by a generator or alternator which delivers an electrical charge to the battery while the engine (gas or diesel) is running. The generator or alternator must be regulated to ensure that a sufficient charge arrives at the battery and yet avoids an overcharge which would cause electrolysis and a possible explosion.
Storage batteries have been known for years and they can be made from numerous combinations of metals for electrodes and chemicals for electrolytes. Improvements have consisted of changing the composition of the electrodes, rearranging the inner construction of the cell, or changing the electrolyte. Electrode composition has included zinc, copper, silver, gold, nickel, cadmium, iron and various other mixtures of metals. Electrolyte composition has included sulfuric acid, potassium hydroxide, zinc hydroxide, sulfuric and other electrolytes.
Recent improvements have included modified vent caps for each cell that trap most of the evaporated water, allowing the water to condense and drain back into the case. Batteries are also often fully sealed to prevent water from escaping. Such batteries include empty spaces within the case to accommodate the buildup of hydrogen gas. Previous batteries had vent caps that allowed water vapor to escape which allowed the sulfuric acid solution to become too acidic, thereby corroding the plates. Other improvements directed to the plates include lead-calcium alloy plates and special plate coatings such as Teflon to help the plates resist corrosion. Also, improvements such as strengthening and encapsulating plates to prevent electrical shorts due to vibration have been implemented. The Battery Council International states that the average car battery life is 31/2years. Even with the improvements mentioned above, car batteries manufactured under current technology last approximately 7 years.
The fact remains, however, that little has changed in the fundamental design of storage batteries since Gaston Plante invented the battery cell in 1860. Present day batteries, while having longer life than earlier models, must still be almost constantly recharged. These batteries are also heavy, cumbersome, limited in the number of volts produced, limited in the current produced, and potentially dangerous. The batteries cannot deliver a sustained, predictable, reliable source of power over time and are essentially and fundamentally inefficient. These batteries consume far more energy during recharging than they can ever generate. The cost of energy production from such a source is high. Thus, the applications for such batteries are severely restricted.